1. Field of the Invention
The present invention relates to a pneumatic tire in which wet performances and noise performances have been improved while restricting degradations in steering stability on dry road surfaces (dry performances).
2. Description of the Prior Art
In pneumatic tires for use in passenger cars or the like, tread grounding surfaces are generally provided with main grooves extending successively in a tire peripheral direction, wherein wet performances are improved by increasing groove capacities of such main grooves so as to shift velocities at which hydroplaning and others occur to a higher speed region.
However, when the groove capacities of the main grooves are set to be large, drawbacks are presented in that large air column resonance is generated through air passing through air column tubes formed by the main grooves and the road surface when running on a dry road surface, and in that noises inside and outside of vehicles are increased. In this manner, there exists a contradictory relationship between wet performances and tire noise so that it is strongly being wanted for tires in which both features are improved.
The applicant of the present invention has thus suggested in Japanese Patent Laid-Open Publication No. 2003-285610 to form main grooves of large width at positions separate from a tire equator by specified distance and to make both groove side edges of the large width main grooves succeed in a linear manner in the tire peripheral direction without being interrupted by lateral grooves or sipings. In such a tire, it is possible to improve the wet performances by setting the main grooves to be of large width. Further, since both side edges of the main grooves are linearly successive, air column resonance will be hardly excited. Moreover, since the main grooves are formed at portions at which they are exposed to low grounding pressure, effects such as improving the noise performances such as restricting air column resonance low can be exhibited.
However, since the main grooves of large width are provided at non-symmetric positions in such a tire, the grounding balance may be affected which may bring on the fear that the dry performances are degraded. Particularly in case sipings are formed for securing steering stability (on-snow performances) on snowy road surfaces, further degradations in dry performances are worried owing to decreases in pattern rigidity.